A broad variety of new demands is being placed on the electromagnetic spectrum, leading to difficulty in allocating radio wave frequency bands as new kinds of equipment based on radio wave communication are developed. Such demands provide pressure to employ progressively higher radio frequencies (e.g., &gt;500 megahertz) and need to utilize spectral space more efficiently. These trends create requirements for frequency selection components capable of high frequency operation and increasingly narrow passbands. Additionally needed are devices having low insertion loss coupled with improved out-of-band signal rejection, in a small form factor and with low power consumption.
Acoustic wave devices are becoming particularly important in the construction of electronic signal processing equipment, such as radios, paging devices, and other high frequency electronic apparatus, because they can be readily constructed on planar surfaces using integrated circuit fabrication techniques, are robust and compact, require no initial or periodic adjustment and consume no static power. Thus, SAW resonators and other types of acoustic wave frequency selection components are extremely desirable for high frequency filtering applications.
The surface vibrations that cause these devices to have extreme utility in modern communications apparatus lead to packaging constraints that differ from those of most microelectronic components. These vibrations are damped (and the frequency selection characteristics impaired or destroyed) by the presence of surface contamination and especially by condensation of liquids on the device surface. Typically this is obviated by employing hermetic packages that do not physically touch the active device surface. As a result, it has been difficult or impossible to provide packages for these devices using technologies (e.g., transfer molding) that have been developed for other types of microelectronic parts.
A second problem that hermetically sealed packages engender is that the finished, packaged device is much larger than the SAW device die. A reduction in size and/or weight of the completed frequency selection component provides significant advantages in the applications for which these devices are designed, such as portable telephones, paging apparatus and the like.
A third problem that arises is that hermetic packages typically include a higher labor content than, for example, transfer molded packages. This, in turn, is reflected in the total labor content of the completed communications apparatus in which these devices are used.
What are needed are apparatus and techniques for acoustic wave device packaging that provide a small, light-weight device package having an open area above the die surface, that do not require substantial internal volume and that are easily implemented in a fashion consistent with current acoustic device design, fabrication and use practices.